JPS6281977A - Current balancer for series connection type dc-dc converter - Google Patents

Abstract

PURPOSE:To inhibit the unbalance of currents without resulting in the scaling-up of a device and the lowering of efficiency by inserting a nonlinear resistor to an input circuit in common to adjacent DC-DC converters. CONSTITUTION:Transistors 14, 24 for two pairs of DC-DC converters connected in series receive base signals simultaneously conducting ON-OFF operation from comparators 18, 28. A non-linear resistor 31 is inserted to an input circuit in common to both DC-DC converters. Unbalanced currents generated by the discrepancy of the actual operation of the transistors 14, 24 are inhibited by the non-linear resistor 31.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical alter ego to which the invention pertains] This invention provides a loosely balanced device l for suppressing the unbalance of the input 'i[4] of a DC-DC converter used in series connection.
Regarding this.

[Prior art and its problems]

Fig. 4 is a main circuit connection diagram showing a conventional example of a DC-DC converter connected in series, and in this Fig. 4, the input side of a 2m ringing choke type DC-DC converter is connected in series. However, such a series connection is adopted when the input DC' voltage exceeds the withstand voltage of the switching element.

In Fig. 4, by connecting two input capacitors 12 and B of equal capacity in series and connecting them to the DC power supply l, the power supply voltage E is divided into v2 for each capacitor, so this input If a ringing DC-DC converter is connected in parallel to capacitors 12 and 4, the input voltage of each DC-DC converter will also be V2.

The DC-DC converter of the positive electrode 1111 is connected to the 1 of the transformer 13.
The next winding and the transistor 14 as a switch element are connected in series, and similarly in the DC-DC converter of the negative pole 1, the primary winding of the transformer and the transistor U as a switch element are connected in series. Because it is connected to.

By turning on both of these transistors 14 and 2 at the same time, current flows and energy is stored in the primary winding of the transformer 13. Next, when both the transistors 14 and the transistors are turned off at the same time, the energy stored in the above-mentioned primary windings is taken out from the secondary windings of each transformer 13 and the secondary windings of the transistors 14 and 2 via the diodes 15 and 5, respectively. So 1
If the output sides of both DC-DC inverters are connected in parallel, DC power smoothed by the output capacitor 2 can be supplied to the load 3. However, with this circuit configuration, the input capacitors 12 and 22 connected in parallel to f
, the equivalent impedance of the knee DC-DC converter is balanced.

FIG. 5 is an operation waveform diagram showing the operation of each part of the conventional example circuit shown in FIG. 4, in which FIG. DC- on the positive side
The waveform of the DC converter input current Ill is shown in Figure 5 (c).
is the voltage (VlO) waveform of transistor 14.

FIG. 5(b) shows the waveform of the DC-DC converter input current I21 on the negative side, and FIG. 5(e) shows the waveform of the voltage v2 of the transistor.

Ir
[The magnetic pressure and current waveforms in the FIDC-DC converter are the same, and the operations described below are repeated.

That is, by turning on the transistors 14 and 24 for a period T1, a voltage E of the current fLl is applied to the transformer 1:) J and the respective primary windings of the input capacitor 12 and ρ.
A voltage V2 divided into two equal parts is applied to IJa, and energy is stored in these transformers 13.

If the inductance value converted to the primary illumination of each transformer 13 is L, then the input current Ixt of the DC-DC converter on the positive side and the input current I2 of the l) C-DC converter on the negative side. is expressed by the following formula (11).

Tatashi I. is the current immediately after the transistor 14 and Sae are turned on, and t is the elapsed time after these transistors 14 and Sae are turned on.

Next, when the transistors 14 and Sae are turned off, the energy stored in the transformers 13 and 2 is released through the diodes 15 and 5, respectively, so the voltage of the output capacitor 2 is changed to vo, and the voltage of the transformer 13 and the If the turns ratio of the primary winding and the secondary winding is N1:N2, the voltages v1 and v2 applied to the transistor 14 and the transistor 14, respectively, are as follows (
2) It is rained down by the formula.

Here, V is a jump voltage caused by the inductance of the wiring, and has the largest value at the moment when the transistor 14 and the capacitor are turned off, and then rapidly attenuates to zero. Transistor 14 and Sae are off at 1゛2
After that, it repeats on and off again, but by changing the ratio between the on period T1 and the off period T2, the voltage vo on the output side can be changed.

By the way, in the important DC-DC converter, it is impossible to make each circuit constant and the switching and NANG operations of the transistors exactly the same, so 1! This causes an imbalance in pressure and current. When using a transistor as a switching element, the off delay time (hereinafter referred to as accumulation time) due to the gear+1 gear accumulation effect is approximately 10 to 20 microseconds, and this accumulation time may vary depending on individual differences between transistors. Also causes variation. Therefore, when the operating frequency of the DC-DC converter is good or when the current flow rate of the transistor is small, the difference in storage time for each transistor cannot be ignored compared to the conduction time, so The unbalance of voltage and current becomes noticeable. That is, the current in the lJc, -DC converter, which is composed of transistors with a long storage time, becomes large.

Furthermore, since the length of this accumulation time depends on the magnitude of the current at turn-off, the longer the current becomes, the longer the accumulation time becomes, resulting in the following inconvenience.

One D is composed of transistors with a long storage time.
Since one DC-DC converter is supplied with energy from the power source for a long time, the current is larger than the other DC-DC converter.
Since the output sides of the converters are connected in parallel, the sum of the output currents of the respective DC-DC converters is the load current, which is a constant current. Therefore, if the turn-off current of one transistor becomes small, the turn-off current of the other transistor will inevitably become small, and the difference in storage time will further increase, which will further increase the current imbalance. .

When the direct current becomes unbalanced, the voltage sharing between the input capacitor 12 and the capacitor becomes unbalanced. That is, since the voltage of the input capacitor connected to the DC-DC converter having a transistor with a long storage time decreases, the current flowing through the DC-L)C converter is reduced. The input capacitor voltage on the other side (i.e., the 9111 with the short storage time transistor) rises and the DC-
Increase the current of the DC converter.

By repeating the above operation, current is exchanged between both DC-DC converters, that is, current hunting occurs, and in the worst case, for a certain period of time Lt, one DC-DC
The DC converter will also share all of the load current. Therefore, an excessive current will flow compared to when operating in a balanced state, so the equipment constituting the DC-DC converter, especially the transistors 14 and 24.
A large flow capacity is required. Furthermore, the value of the jump voltage v1 that occurs when interrupting this large current flowing through the wiring inductance also becomes large, so the snubber circuit shown in the diagram also needs a large capacity one, which increases the loss and causes various problems. It's inconvenient.

Therefore, if an attempt is made to suppress the current imbalance by inserting a reactor or a resistor in series with the transistor 14 and the transistor 14, if a reactor is inserted, the voltage will jump up when the transistors 14 and 24 are cut off due to the energy stored in the reactor. v5 becomes even larger and a snubber circuit with a larger capacity is required, and if a resistor is inserted, power is consumed by this resistor, which reduces the effectiveness of the device and increases heat generation due to power consumption. It has drawbacks such as the need to take measures to dissipate it.

[Purpose of the invention]

The present invention provides a series-connected DC-DC converter that can suppress current imbalance occurring in a plurality of series-connected DC-DC converters without increasing the size of the device or reducing efficiency. The purpose is to provide a current balancing device.

[Key points of the invention]

In this invention, when current unbalance occurs between a plurality of series-connected L)C-DC converters, adjacent D
This method focuses on the fact that current flows through an input circuit common to C-L)C converters, and a non-linear resistor is inserted into this common input circuit, and the current flowing through this non-linear resistor due to current imbalance is If it increases, it will automatically and rapidly l
The unbalanced current is suppressed by increasing the resistance value of this nonlinear resistance and suppressing this current.

[Embodiments of the invention]

The first factor is a circuit diagram showing an embodiment of the present invention, in which two sets of DC-DC converters are connected in series. Explain.

In Figure 1 E, 211! input capacitors 12 and n
A series circuit is connected to the DC power supply l to divide the power supply voltage for each capacitor. One DC-DC converter composed of a transformer 13, a transistor 14 as a switching element, and a diode 15 is connected in parallel to the input capacitor 12, and a transformer n, a transistor 14 as a switching element, a diode δ, The other DC-DC converter consisting of L) is connected in parallel to the input capacitor a, and the output sides of these two L) C-DC converters are connected in parallel with each other, and then connected to the load via the output capacitor 2: It is designed to supply power to 3.

Since the deviation value between the voltage setting value outputted by the voltage setting device A and the voltage output value obtained from both ends of the output capacitor 2 is input to the voltage regulator A, this voltage setting device Akara calculates the input deviation value. A zero control signal is output to the comparator 18 and the column. On the other hand, the comparator 18 also receives a triangular wave signal of a predetermined frequency formed by one oscillator and the triangular wave generator 37.
and 4, the comparator 18 and the gate separately compare the magnitude relationship between the two power counts, thereby creating a pace signal that turns on and off the transistor 14 and the power bank.

As described above, the transistors 14 and 2 of the two series-connected DC-DC converters receive base signals that should be turned on and off at the same time, but due to the difference in accumulation time, their actual operations are the same. However, in the present invention, a non-linear resistor 3 is installed in the input circuit common to both DC-DC converters.
1 is inserted, the current XL flowing through this nonlinear resistor 31 due to current imbalance is suppressed. In addition, L
is the current 1. This is the voltage generated across this non-linear resistance 31.

FIG. 2 is an operational circuit diagram explaining the operation corresponding to the on/off state of each transistor in the embodiment circuit shown in FIG. Figure 2 (b) shows mode B, in which transistor 14 is turned off first, and each transistor is still in conduction due to the difference in storage time. Figure 2 (c)
represents mode C1, that is, a mode in which both transistors 14 and 24 are off. Note that this second
In the figure, it is assumed that the storage time of the transistor 24 is longer than that of the transistor 14. Furthermore, in order to simplify the circuit board, load 3. transistor 1
4 and 5, diodes 15 and 5, a transistor control circuit, etc. are not shown.

Here, the operation of each mode will be described below, but to simplify the explanation, it is assumed that the circuit constants of both DC-DC converters are equal.

(a) Mode A: Since both transistor 14 and transistor are conducting, current Ill flows through the primary winding of the transformer 1:1.
However, the current I21 flows through the primary winding of the transformer C, and energy is stored in each of the transformers 13 and 1.

At this time, since the voltages shared by the input capacitors 12 and n are equal, the currents ■□l and 121 have the same value, and the value of the current IL flowing through the nonlinear resistor 31 is zero.

(b) Mode B: This is a mode in which one transistor 14 is off but the other transistor is still in a conductive state due to the difference in storage time, and at the same time when the transistor 14 is turned off, the primary winding of the transformer 13 The current Ill flowing in the line is transferred to the secondary winding, and the energy stored in the transformer 13 is released to the secondary side as a current ■1□. At this time, the other transistor 14 is still in the 44 state, so at the same time as the transistor 14 is turned off, the primary winding current I2□ of the transformer is connected to the nonlinear resistance 31-f voltage field.
It will continue to flow through the path of the transistor Sae. Since the resistance value of the non-linear resistor 31 is always a very small value,
When the current value and the current flowing time in mode B are small, that is, when I2@t is small, the energy consumed by this nonlinear resistor 31 is small, so no change in resistance occurs, but both If the difference between the storage times of the transistor 14 and the storage time is large, 1 -1 in this mode B will also be large, and the energy consumed by the nonlinear resistor 31 will increase. Due to this increase in energy consumption, the resistance value of the non-linear resistor 31 rapidly increases, so the shared voltage vL of the non-1 page line resistor 31 suddenly increases, resulting in a phenomenon similar to that of a transistor being turned off. state. Therefore, current ■2□ will flow in the secondary side of the transformer path on the side that has been delayed in turning off, and the stored energy in this transformer path will be released.

(C) Mode C: Since both the transistor 14 and the current are off, the inflow current of the transformer 13 is the current 112 from the secondary winding, and the inflow current of the transformer path is the current 112 from the secondary winding. The current I22 is completely transferred and these transformer stored energies are released to the load side.

FIG. 3 is an operation waveform diagram showing the operation in each mode shown in FIG. 2 in the embodiment circuit shown in FIG.
A) shows the on/off state of the transistor 14, and FIG.
B) shows the on/off state of the transistor Sae; Figure 3 H]
(The waveform of the primary current Ill of the transformer 13 is shown in Fig. 3.)
is the waveform of the secondary current fiIt2 of each transformer, FIG. 3(G) shows the waveform of the current IL flowing through the nonlinear resistor 31. FIG. Also in FIG. 3, it is assumed that the storage time of transistor U is longer than that of transistor 14. Furthermore, the broken line shown in FIG.
The solid line portions in Figure 3 (E), (F), and (G) are shown in contrast.

(As is clear from the figure, in mode B, where one transistor 14 is off and the other transistor is on, the nonlinear resistance 31
When a current of 1L flows, the resistance value of the non-directly connected resistor 31 increases rapidly due to this current It+, so it has the same effect as turning off the transistor U, and the current due to the difference in accumulation time increases. effectively suppress the imbalance.

The above embodiment is a two-stage series-connected ringing chain.
In the case of a C-DC converter, current unbalance must be avoided in the case of multi-stage series connection, in the case of multi-stage series connection of forward type DC-DC converters, or in the case of parallel or series connection of the secondary side. Of course, the present invention can be applied to suppress this.

〔Effect of the invention〕

According to this invention, when operating a plurality of DC-DC converters whose input sides are connected in series to cope with high power supply voltages, the current generated due to the difference in storage time of the switch and tee elements of each converter To prevent unbalance and current hunting, by inserting a non-linear resistor into the common input circuit of adjacent DC-DC converters, unbalance IIt can be avoided.
When current flows through this non-linear resistance l, the resistance value rapidly increases by l, producing the same effect as opening a switch element whose off-time has been delayed, thereby suppressing unbalanced current. The energy consumed by this non-linear resistor is only the unbalanced portion of the current, and unlike a normal balance resistor, energy corresponding to the circuit current is not consumed. Therefore, the energy consumed by this non-linear resistance is small, hardly reducing the efficiency of the device, and the unbalanced current can be effectively suppressed with a small size and low cost.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is an operational circuit diagram illustrating the operation corresponding to the on/off state of each transistor in the embodiment circuit shown in FIG. 1, and FIG.
This figure is an operation waveform diagram showing the operation in each mode shown in FIG. 2 in the embodiment circuit shown in FIG. 1. FIG. 4 is a main circuit connection diagram showing a conventional example of a DC-DC converter connected in series, and FIG. 5 is an operational waveform factor showing the operation of each part of the conventional example circuit shown in FIG. l...DC power supply, 2...output capacitor, 3...
Load, 12, 22... Input capacitor, 13, 2
3...Transformer, 14, 24...Transistor as a switch element, 15, 25...Diode, 1
8, 28... Comparator, 31... Non-linear resistance, A... Voltage setting device, A... Voltage regulator, 36...
- Oscillator, 37... triangular wave generator. 11th!1

Claims (1)

[Claims] 1) DC that can extract power from the secondary winding of the transformer by applying a direct current to a series circuit of the primary winding of the transformer and a switch element, and turning on and off the switch element. - A series connection type D consisting of a plurality of DC converters connected in series with each other on their input sides and with the output sides of each DC-DC converter connected with each other.
In the C-DC converter, the adjacent DC-DC
A current balancing device for series-connected DC-DC converters, characterized in that a non-linear resistance is inserted into an input side circuit common to the converters.